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slow cooling advice needed

updated sat 26 feb 05

 

primalmommy on tue 22 feb 05


I have several questions to sort out here regarding slow cooling in an
electric kiln.

I don't have a kiln with the 3 switches -- in which case I could figure
this out easily -- nor do I have a computer controller, which would be a
piece of cake to slow cool. I have an Evenheat kiln with a fire-right
timer, which is somewhere it the middle. I can set it for how quickly to
ramp upward, (at least how many hours to get to 100 percent power) and
it is shut off by the kiln sitter with a timer for a backup.

1.) I have one of the cheap but useful axner pyrometers, but while I
hesitate to leave the thermocouple in the peephole for the entire
firing, it would be tricky to poke it through that narrow hole in mid
firing without sprinkling crap on my glazed pots. Any ideas on whether
to leave it in? And how far in?

2.) Once the kiln shuts itself off via the kiln sitter cone, if I can
catch it in time, I can re-push the button, let the trigger down slowly,
set my timer to an hour or half hour or something and set the power on
either low, medium or high. The times I have successfully managed to
soak, the glazes have been lovely. I need repeatable results, though.
Low, medium or high? And at what point in the cooling down ramp should I
hold? (I'm several states away from my M^6 book and can probably find
that info there tomorrow when I get home.)

3.) So far my approach has been to leave a baby monitor next to the kiln
and carry the receiver with me, so that when I hear the "pop" of the
kiln sitter I can go out and re-start it. (Kiln is in a cinder block
garage, not my home or studio.) The problem now is that I have installed
a kiln vent, and it is pretty noisy - I can't stand to walk around
listening to it via the baby monitor. I talked to mel about his light
bulb system, but I hesitate to mess with the wiring of a kiln that might
still be under warranty. The time it takes to fire varies, based on how
full the kiln is, as well as other variables I haven't figured out
(maybe like whether it's 20 below zero? Or the neighborhood drain on the
power source at 3 am or 3 pm?)

4.) Kiln vent: I have a hard time figuring out the effect of a kiln vent
on firing and cooling. I so carefully drilled just the right sized
holes, but now that my kiln lid bows upward in front during firing, what
the hell difference does the size of the drill bit make? There's half an
inch of grin with air sucking in now.

My vent (rtfm, right?) says it can't be left off during firing or the
motor will cook. Aside from the noise/monitor problem, I don't mind
that. But it also says it can be shut off when the firing is over (at
peak temp? Go figure) -- and the process is complicated by the amount of
time it takes the lid to lie down and behave once it begins to cool.

There must be other potters out there who have mastered some slow
cooling procedures who can make suggestions. The easy answer is "get an
external computer controller", which may be my next clay paycheck (the
last one is committed to NCECA). In the meantime, I am open to any
suggestions.

Yours
Kelly, last day in Florida, back to the snow/ice/overflowing cat litter
boxes tomorrow...








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Craig Clark on tue 22 feb 05


Kelly, I can sort of help you out with the cool down. I don't have a
computer on my Skutt (1027) and have managed to figure out a pretty good
procedure that gives consistent results. The difference is that I have
three potentiometers on the kiln that I'm able to adjust form
Low/Med/High. However, the fundamentals of the procedure should work for
you as well.
You probably have a pretty good idea about how long it will take for
your kiln to trip the kiln setter when you are getting towards the end
of the firing. Just hang out with the kiln for the last hour or so and
keep a good eye on things.I suggest that you give up the baby monitor
sound relay at this point. An organic interface is pretty necessary at
this point in the operation. Monitor your progress with LRB cones in the
kiln that you can see as well. These are critical for good firing. They
will really let you know where you are with your melt. Also pay
attention to the color of the atmosphere. It will give you an indication
of your fire down as you become more accustomed to doing this.
Assuming that you are firing to cone6 do the following. As soon as
the kiln sitter trips just lift the mechanism a press the button in. At
this point it is advisable to not leave the kiln until you are sure that
you are in the FIRING DOWN stage. You aren't there yet unless your kiln
sitter is very well calibrated. Check the LRB cones in the kiln to see
where you are and also look at the temp on your pyrometer. Make careful
notes. Continue firing until the tip of the cone6 cone is touching the
cone pat and then try and hold the temp for about thirty minutes. You
will need to try swithcing back and forth between low and medium or
possibly even a couple minute bumb back to high to get this to work.
It's something you will need to develop a feel for but you can do it.
After about a thirty minute soak just set the controller to low and
let the temp drop down to about 1900F. I used to only let it go down to
2100F but John says 1900 is the place to be. You will be monitoring your
pyrometer for this. Keep notes, observe. The time this takes will change
from load to load. At 1900F start your slow decent. You will need to
bump some energy back into the kiln to do this. Try setting the
controller back to high and watch your pyrometer over the next several
minutes. It should stop falling and the temp should begin to climb again.
At that point try backing off your controller to medium and see what
the temp does. Try and keep the drop at less than 100F/hr all the way
down to 1400F. I try and keep it between 50F and 75F drop per hour. If
you look at Johns page and the tests on Waterfall Brown you will see
their differing results. YOu will be able to customize this to suit your
needs.
The key to this is getting to know how your kiln responds to the
various settings. After a few attempts you will begin to develop a sense
for what you need to do. Just experiment in a structured calculated
manner and keep detailed notes.This is different than the firing of an
electric kiln where we have been able to turn it on and basically leave
it. It leaning back in the direction of firing a gas kiln which requires
monitoring and adjustments.
Hope this helps
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org

Arnold Howard on tue 22 feb 05


Kelly, I suggest that you call your kiln manufacturer about the lid rising
in the front. I'm sure they didn't design the lid to do that, and they
probably have an easy solution.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
arnoldhoward@att.net / www.paragonweb.com

----- Original Message -----
From: "primalmommy"
> 4.) Kiln vent: I have a hard time figuring out the effect of a kiln vent
> on firing and cooling. I so carefully drilled just the right sized
> holes, but now that my kiln lid bows upward in front during firing, what
> the hell difference does the size of the drill bit make? There's half an
> inch of grin with air sucking in now.

dannon rhudy on tue 22 feb 05


Kelly, you do NOT have to have a computer controller to
slow cool. You are making it harder than it is. Just watch
the kiln, (leave the pyrometer IN the kiln during the
firing). You can turn it off if you want your battery
to last longer, when you're not there to see it. If you got
a ceramic cover for the probe, good. If not, it will still
last quite some time. So USE it, already.

When the kiln reaches temp, start it back up again when
it's cooled to 1900 or so, then dink with the switch(es)
while you watch the pyrometer. Turn it up until it continues
to cool, but the cooling is slowed. Not hard, I swear.

regards

Dannon


----- Original Message -----
From: "primalmommy"
To:
Sent: Tuesday, February 22, 2005 8:22 AM
Subject: Slow cooling advice needed


> I have several questions to sort out here regarding slow cooling in an
> electric kiln.
>
> I don't have a kiln with the 3 switches -- in which case I could figure
> this out easily -- nor do I have a computer controller, which would be a
> piece of cake to slow cool. I have an Evenheat kiln with a fire-right
> timer, which is somewhere it the middle. I can set it for how quickly to
> ramp upward, (at least how many hours to get to 100 percent power) and
> it is shut off by the kiln sitter with a timer for a backup.
>
> 1.) I have one of the cheap but useful axner pyrometers, but while I
> hesitate to leave the thermocouple in the peephole for the entire
> firing, it would be tricky to poke it through that narrow hole in mid
> firing without sprinkling crap on my glazed pots. Any ideas on whether
> to leave it in? And how far in?
>
> 2.) Once the kiln shuts itself off via the kiln sitter cone, if I can
> catch it in time, I can re-push the button, let the trigger down slowly,
> set my timer to an hour or half hour or something and set the power on
> either low, medium or high. The times I have successfully managed to
> soak, the glazes have been lovely. I need repeatable results, though.
> Low, medium or high? And at what point in the cooling down ramp should I
> hold? (I'm several states away from my M^6 book and can probably find
> that info there tomorrow when I get home.)
>
> 3.) So far my approach has been to leave a baby monitor next to the kiln
> and carry the receiver with me, so that when I hear the "pop" of the
> kiln sitter I can go out and re-start it. (Kiln is in a cinder block
> garage, not my home or studio.) The problem now is that I have installed
> a kiln vent, and it is pretty noisy - I can't stand to walk around
> listening to it via the baby monitor. I talked to mel about his light
> bulb system, but I hesitate to mess with the wiring of a kiln that might
> still be under warranty. The time it takes to fire varies, based on how
> full the kiln is, as well as other variables I haven't figured out
> (maybe like whether it's 20 below zero? Or the neighborhood drain on the
> power source at 3 am or 3 pm?)
>
> 4.) Kiln vent: I have a hard time figuring out the effect of a kiln vent
> on firing and cooling. I so carefully drilled just the right sized
> holes, but now that my kiln lid bows upward in front during firing, what
> the hell difference does the size of the drill bit make? There's half an
> inch of grin with air sucking in now.
>
> My vent (rtfm, right?) says it can't be left off during firing or the
> motor will cook. Aside from the noise/monitor problem, I don't mind
> that. But it also says it can be shut off when the firing is over (at
> peak temp? Go figure) -- and the process is complicated by the amount of
> time it takes the lid to lie down and behave once it begins to cool.
>
> There must be other potters out there who have mastered some slow
> cooling procedures who can make suggestions. The easy answer is "get an
> external computer controller", which may be my next clay paycheck (the
> last one is committed to NCECA). In the meantime, I am open to any
> suggestions.
>
> Yours
> Kelly, last day in Florida, back to the snow/ice/overflowing cat litter
> boxes tomorrow...
>
>
>
>
>
>
>
>
>

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John Post on tue 22 feb 05


Hi Kelly,
Here is a post that I sent to clayart a while ago about slow cooling =20
without a controller.
------------------------------------------------------------------------=20=

------------------------------------
Several years ago I was having some discussions with Jan Walker about =20=

iron
red glazes. I began experimenting with controlled cooling in order to =20=

get
a redder color and more metallic sparkle in the glazes.

I found that many of my glazes benefited from a slow cooling especially =20=

a
high calcium matte glaze base that I use frequently

I fire to cone 6 with a computer controller in my studio. After I reach
cone 6, I let the kiln drop to 1800 degrees F. Then I use the computer =20=

to
drop it 150 degrees per hour until I hit 1300 degrees F and then I let =20=

the
kiln cool on its own again.

As an elementary school art teacher, I wanted to duplicate this firing
schedule at my school. The problem was that the kilns I have do not =20
have a
computer controller on them.

I have found a work-around method that I have been using all year.

I have a 6 cubic foot paragon kiln with a kiln sitter and two switches =20=

that
are the low-med-high type. I noticed that when both switches were set =20=

to
medium the kiln would reach red heat, but not get hot enough to reach =20=

cone
6. When I leave the building for the day, I turn both switches to =20
medium
and the limit timer to the max setting. When I come in the next =20
morning the
kiln is at red heat. Then I turn both switches to high. It takes =20
about 3-4
hours for the kiln to reach cone 6 and for the sitter to drop.

Then I lift the sitter plunger, push the button in again and lower the
plunger slowly.
I turn both switches DOWN TO MEDIUM and set the limit timer for 4 hours.
This gives the kiln a four-hour soak in the red heat range. The calcium
mattes look as good as they do at my home studio with the controller.

For my glazes it appears as though it is not that important that they go
from 1800-1300 F at a controlled rate=85as long as long as they are =20
somewhere
in that red heat range for 4 hours during cool down they turn out fine.

I have a smaller 3.3 cubic foot kiln with the on-off type switches and =20=

when
3 out of the 5 switches are turned on I can maintain red heat in that =20=

kiln
and get the same kind of effect with it.

I am sharing this information for those that may wish to try the slow
cooling technique.

A computer controller is the way to go, but if you don=92t have one, =
this
method yields similar results for me.
------------------------------------------------------------------------=20=

-----------------------------

I would add that it is ok to leave the thermocouple in for the entire =20=

firing.
Kiln controllers are run by thermocouples that are in for the entire =20
firing and they hold up ok.

As far as the gap at the front of your kiln, if you have a small enough =20=

lid to lift on and off, you can remove the back hinge.
I found that on one of my smaller kilns the hinge was actually =20
preventing the lid from laying flat on top of the kiln.
Also you can then shift the lid around to different positions and one =20=

might actually fit better.

As far as the kiln vent goes, I teach in an elementary school and I did =20=

a firing right before we had a week long vacation.
I left the kiln vents on for an entire week after firing two kilns =20
before break. I've done this in the past and haven't had any
problems with the kiln vents.

If you have any questions or something isn't clear, let me know.

Cheers,
John Post
Sterling Heights, Michigan=

Crystal Nolfo~Brown on fri 25 feb 05


I also have one of those kilns that have switches. You could switch yours
to medium and soak like the previous post said. That's what I do. When my
kiln reaches peak I don't hold that temperature because my kiln takes so
long to get there in the first place that it is already
considered "soaked". You may try what I did but it is a lot of work for a
day. So that I knew exactly what to expect from my kiln I went out every
1/2 hour to 1 hour and charted the temperature rise and temperature fall.
This information tells a lot and is a very worthwhile thing to do. I
charted the temperature fall in cool down and found that when I switched my
kiln to medium that the temperature dropped quickly to around 1900=B0F but
once it got to that temperature the fall wasn't so rapid. Perfect. That's
exactly what I want it to do. As the temperature got progressively lower
the temperature fall rate was less and less till it would hold the
temperature. At that point I could switch to low setting and again the
temperature drop was increased but slowed to a certain point. Now I know
exactly what to expect from my kiln. This gave me a great playing area that
I could alter other ways later. At least I had the original firing to
always go back on. From there I charted many other firings and varied the
times that I switch the kiln. This way when I finally get the perfect
firing I can duplicate it.

Oh by the way. I also have the Axner Pyro and leave it in the kiln all the
time. That way it is in the same distance inside the kiln so the readings
are consistant.

Good luck,
Crystal Nolfo~Brown
Louisiana, USA

Gaye Sekula on fri 25 feb 05


I want to second everything that Crystal Nolfo-Brown said about slow
cooling. My 30 year old kiln reaches ^6 at a slow, steady and predictable rate,
which I also feel is the equivalent of a soak. Once it has reached temperature, I
turn all of my six switches to medium. When the temperature stops dropping I
slowly turn them down even further until it reaches between 1500F & 1600F,
depending on my patience for the day. From the time it reaches ^6 to the time
it gets to 1500F-1600F is approximately 4 hours.
I would also like to stress the value of keeping accurate temperature
records. I also monitor and record the temperature every hour on the hour. It is
your very first indicator when elements begin to show substantial wear or if
connections aren't as they should be. I also use witness cones on the top,
middle and bottom shelves. That way I know if the kiln is firing evenly and, if
there is a temperature discrepancy, I know which area of the kiln to trouble
shoot. Oh, and I also use a pyrometer, but only as an indicator of the
progression of firing. It's very helpful in getting an idea of when that first cone
should begin falling and letting you know it's time to stay around.
You don't need a computerized OR a new kiln to be able to follow a good
schedule. You do have to be around to monitor things more closely, but I would do
that even with a computerized kiln.
Gaye Sekula
Sekula Pottery
San Antonio, Texas